Example 1: C++ Program to convert binary number to decimal

#include <iostream>
#include <cmath>

using namespace std;

int convertBinaryToDecimal(long long);

int main(){
    long long n;

    cout << "Enter a binary number: ";
    cin >> n;
 
    cout << n << " in binary = " << convertBinaryToDecimal(n) << "in decimal";
    return 0;
}

int convertBinaryToDecimal(long long n){
    int decimalNumber = 0, i = 0, remainder;
    while (n!=0)
    {
        remainder = n%10;
        n /= 10;
        decimalNumber += remainder*pow(2,i);
        ++i;
    }
    return decimalNumber;
}

Output

Enter a binary number: 1111
1111 in binary = 15

Example 2: C++ Program to convert decimal number to binary

#include <iostream>
#include <cmath>
using namespace std;

long long convertDecimalToBinary(int);

int main(){
    int n, binaryNumber;

    cout << "Enter a decimal number: ";
    cin >> n;
    binaryNumber = convertDecimalToBinary(n);
    cout << n << " in decimal = " << binaryNumber << " in binary" << endl ;
    return 0;
}

long long convertDecimalToBinary(int n){
    long long binaryNumber = 0;
    int remainder, i = 1, step = 1;

    while (n!=0)
    {
        remainder = n%2;
        cout << "Step " << step++ << ": " << n << "/2, Remainder = " << remainder << ", Quotient = " << n/2 << endl;
        n /= 2;
        binaryNumber += remainder*i;
        i *= 10;
    }
    return binaryNumber;
}

Output

Enter a decimal number: 19
Step 1: 19/2, Remainder = 1, Quotient = 9
Step 2: 9/2, Remainder = 1, Quotient = 4
Step 3: 4/2, Remainder = 0, Quotient = 2
Step 4: 2/2, Remainder = 0, Quotient = 1
Step 5: 1/2, Remainder = 1, Quotient = 0
19 in decimal = 10011 in binary